Surround-View Imaging System

ABSTRACT

The present invention refers to a surround-view imaging system for time-of-flight (TOF) depth sensing applications and a time-of-flight sensing based collision avoidance system comprising such an imaging system. The imaging system for time-of-flight depth sensing applications comprises a lens system, adapted for imaging angles of view (AOV) larger than 120° in an image on an image plane; a sensor system, adapted to convert at least a part the image in the image plane into an electronic image signal; and an evaluation electronics, adapted to analyze the electronic image signal and to output resulting environmental information; wherein the lens system and/or the sensor system are designed for specifically imaging fields of view (FOV) starting at zenithal angles larger than 60°.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. Pat. Application Serial No.16/892,463, filed Jun. 4, 2020, which claims priority to and the benefitof European Patent Application No. 19178290.3 filed Jun. 4, 2019, theentire disclosures of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention refers to a surround-view imaging system fortime-of-flight (TOF) depth sensing applications and a time-of-flightdepth sensing based collision avoidance system comprising such animaging system. Various types of optical systems as well as sensorconfigurations can provide a range of desired zenithal and azimuthalangle combinations for a surround-view time-of-flight depth sensingbased collision avoidance system.

BACKGROUND

In many fields, including security, automotive and robotics, there is anincreasing demand to obtain a surround-view perspective fortime-of-flight depth measurements relative to a given reference point.This reference point typically corresponds to some illumination andimaging system. Depending on the application, this reference point maybe in a stationary position (as it is often the case with securitycameras), or it may be positioned on a moving object (such as anautomobile, a forklift, or a mobile robot).

For obtaining a surround-view image, multiple individual imaging systemsare typically required and they have to be arranged such that theirindividual field of views (FOV) can be combined in the form of apanoramic environmental view. Implementing multiple imaging systemsproduces higher costs, especially when the various sensors are alsoconsidered. Therefore, technical solutions to create a comparablesurround-view image on a single sensor by a single lens system aredemanded. In this context, surround-view means that a 360° panoramicview can be imaged by a single imaging system (at least in principle).

A typical time-of-flight depth sensing system consists of anillumination system including beam forming (e.g. electronic and/oroptical beam forming in a temporal and/or spatial manner), an imagingsystem comprising a receiving optics (e.g. a single lens or a lenssystem/objective) and a sensor for image detection, and an evaluationelectronics for calculating the distances and maybe setting some alarmsfrom the detected image signal. The illumination system typically sendsout modulated or pulse light. The distance of an object can becalculated from the time-of-flight which the emitted light requires fortraveling from the illumination system to the object and back to thereceiving optics.

Optical beam forming can be achieved by a beam shaping optics includedin the illumination system. The beam shaping optics and the receivingoptics can be separate optical elements (one-way optics) or the beamshaping optics and the receiving optics can use single, multiple or allcomponents of the corresponding optics commonly (two-way optics). Suchtime-of-flight depth sensing systems are typically referred to assystems using light/laser ranging and detection (LiDAR/LaDAR).

A surround-view image can be produced by using a wide-angle lens (e.g. a‘fisheye’ lens or rectilinear lens) as the first lens in a lens systemof an imaging system. Wide-angle lenses can have an angle of view (AOV),i.e., the maximum zenithal angle for which a lens can provide an image,of more than 180°. Lenses with an AOV of more than 180° are also calledultra wide-angle lenses. Angles of view up to around 300° can beachieved. In a normal axially symmetric imaging system the imageableazimuthal angle range is typically 360°, which allows surround-view inthe azimuthal direction. Therefore, with an ultra wide-angle lens solidangles Ω of up to around 3π steradiant can be imaged. Wide-angle lensestypically show a strong curvilinear barrel distortion, which can to somedegree optically corrected in rectilinear lenses. An optical barreldistortion correction can also be included in the design of anassociated lens system. Lens systems with an angle of coverage largerthan 180° are called ultra wide-angle lens systems.

A collision avoidance system for ground-based applications often onlyrequires surround view imaging only in a limited zenithal angle rangenear the ground. For collision avoidance system in vehicles, where theoptical axis of the lens system is typically pointing upwards “into thesky”, the lower zenithal angles between 0° and 60° are in most casesonly of minor interest. However, standard wide-angle lens systems aredesigned to provide the best imaging results for the central region ofthe image. In the outer regions, the image often shows only a reducedsharpness and the linearity of the projection becomes low. Even whenapplying elaborate optical correction, aberration effects like enhancedcurvature and optical distortion in the zone of interest (ZOI) aredifficult to handle with standard ultra wide-angle lens systems. Due tothe wide angle of view, object rays are entering the optical system fromall possible directions, causing noise by undesired internal reflectionsinside the lens system. Further, bright sunlight or other intense lightsources outside the ZOI can over-illuminate the senor and decrease thesignal-to-noise ratio (SNR) of the sensor detection. The electronicimage signal of the sensor will thus include the undesired parts of theimage which still have to be processed by the calculation electronicswith some efforts.

The objective problem of the invention is therefore related to theproblem of providing a surround-view imaging system for time-of-flightdepth sensing applications and a time-of-flight depth sensing basedcollision avoidance system comprising such an imaging system which avoidor at least minimize the problems in the prior art. In particular, theinvention refers to a surround-view imaging system in which a range ofdesired zenithal and azimuthal angle combinations for a surround-viewtime-of-flight based collision avoidance systems shall be provided.

SUMMARY

The invention solves the objective problem by at least providing animaging system comprising a lens system, adapted for imaging angles ofview larger than 120° in an image on an image plane; a sensor system,adapted to convert at least a part the image in the image plane into anelectronic image signal; and an evaluation electronics, adapted toanalyze the electronic image signal and to output resultingenvironmental information; wherein the lens system and/or the sensorsystem are designed for specifically imaging fields of view starting atzenithal angles larger than 60°.

Preferably, the lens system is further adapted to image around theoptical axis of the lens system (axially symmetric imaging) in an imageon an image plane perpendicular to the optical axis of the lens system(perpendicular imaging). However, some components of the lens system mayalso be arranged off-axial or the image plane could be shifted and/ortilted with respect to the optical axis of the optical system. Suchembodiments allow an increased flexibility for matching the FOV of theimaging system to a desired ZOI of a specific TOF depth sensingapplication.

The environmental information which is outputted by the evaluationelectronics can be any type of information contained in the imagesignal. In some embodiments only a trigger signal may be outputted asenvironmental information. The trigger signal can be utilized to triggeran external event. In a collision avoidance system for a mobile robot,for example, it may not be required to reconstruct a fullthree-dimensional image (3D image) or a 3D point cloud from the imagesignal. A simple trigger signal correlated to a minimum allowabledistance will be sufficient to avoid a collision by instantly stoppingthe robot. Other types of environmental information may betwo-dimensional images (2D images) or fully reconstructed 3D images or3D point clouds. These images may include optical distortions caused bythe lens system. However, in a collision avoidance system an additionalcalculation of the distances with predefined lens system data could berequired. The evaluation electronics can further output environmentalinformation in the form of identified metadata based on imagerecognition results. In this case the outputted environmentalinformation could also be, for example, an array consisting of twoelements; an object identifier and a numerical value for the distancefrom the reference point to the recognized object.

In some applications, it may also be required to present theenvironmental information to a human. While a collision avoidance systemmay be able to work with 2D images, 3D images or 3D point cloudsincluding optical distortions from the lens system, for a human theseimages should be presented distortion free or distortion corrected.Therefore, the evaluation electronics may be further adapted to correctoptical distortions in the image signal and to output undistorted imageinformation. That means predefined lens system data is used by theevaluation electronics to correct the optical distortions in theelectronic image signal to output environmental information asundistorted image information. For ease in displaying or processing theimage gathered by the sensor, software or an equivalent circuitry may beimplemented in the evaluation electronics to remove the distortion formthe electronic image signal and to form image information with arectangular or trapezoidal format. From the undistorted imageinformation also a distortion-free 3D point cloud may be calculated.

The invention is based on the finding that for most TOF depth sensingapplications using wide-angle lens systems the corresponding ZOI lies infield of views starting at zenithal angles larger than 60°. Lowerzenithal angles ranges may be only of minor importance for suchapplications. As standard wide-angle lens systems are typically designedto provide the best imaging results in the central region of the image,most of the imaging capabilities are wasted for imaging regions outsidethe ZOI. By designing a lens system, for example, specifically forimaging FOV starting at zenithal angles larger than 60°, the lens systemcan be optimized for the relevant ZOI of a specific TOF depth sensingapplication. In particular, the lens system may be optimized to providediffraction-limited imaging for all imaging points in the FOV. Theimaging for zenithal angles less than 60° can be fully neglected in thedesign of a corresponding lens system.

In a preferred embodiment, the lens system is a panomorph lens systemusing panomorph distortion as a design parameter for increasing themagnification of zenithal angles in the field of view compared tozenithal angles outside the field of view. A panomorph lens system isspecifically designed to improve the optical performances in apredefined ZOI. The image of the FOV in the image plane is then enlargedcompared to the image regions outside the FOV. When the image isdetected by the sensing system, the image resolution can thus beenhanced. By using panomorph distortion in the lens system, the imageresolution for a predefined sensor can be optimized by adapting theimage scale to the available sensor surface. Therefore, the lens systemcan be optimized for specifically imaging FOV starting at zenithalangles larger than 60°.

In another preferred embodiment, the lens system is an anamorphic lenssystem adapted to change the aspect ratio of the image in the imageplane. In an anamorphic lens system, cylindrical and/or toroidal lensesare used for non-axially symmetric imaging. Anamorphic designs maybeuseful if a predefined sensor and the image in the image plane showdifferent aspect ratios. Therefore, the sensor may not able to detectthe whole image or parts of the sensor will not be used for imaging,which means that available image resolution is wasted. For matching thedifferent aspect ratios, anamorphic distortion can be integrated in thelens system. Also in this embodiment the lens system can be optimizedfor specifically imaging FOV starting at zenithal angles larger than60°.

In another preferred embodiment, the central region of the entranceaperture of the lens system is covered by a blind. The blind blocks raysentering from undesired small zenithal angles below 60°. Preferably, theblind can be a surface matched (e.g. curved) circular blind, acorresponding elliptical blind or a corresponding freeform blind. Theblind may also cover zenithal angles larger than 60° for some regions.The form of the blind can be used to further define the effective FOV ofthe imaging system, which means that specific zenithal and/or azimuthalangle ranges may be selectively blocked by the blind.

In an alternative preferred embodiment at least a single region otherthan the central region of the entrance aperture of the lens system iscovered by a blind. This embodiment can be can be used to block specificzenithal and/or azimuthal angle ranges by the blind in lens systemswhere another design approach is used for specifically imaging FOVstarting at zenithal angles larger than 60°. In this case, the blindprovides a flexible blocking function.

In another preferred embodiment, the lens system is a catadioptric lenssystem in which refractive and reflective optical elements are combined.A catadioptric lens system is typically used when extremely compact lenssystem designs are required. Further, chromatic and off-axis aberrationcan be minimized within such systems. Preferably, the first lens of thelens system is a biconcave lens element in which object rays arereflected by a single total internal reflection. Also preferred is thatthe first lens of the lens system is a complex freeform lens element inwhich object rays are reflected by two total internal reflections.However, reflections may also occur on surfaces of the lens system whichare designed as metallic or dielectric mirrors.

In another preferred embodiment, the lens system comprises plasticlenses, glass lenses or a combination thereof. Plastic lenses have alower weight and a favorable price compared to standard glass lenses,however, glass lenses can provide a higher optical quality. A lenssystem which combines both types of lens materials can have good opticalquality, a low weight and a lower price compared to lens systemscomprising only glass lenses.

In another preferred embodiment, the sensor system comprises at least asingle 2D sensor, at least a single 1D sensor or a combination thereof.A single 2D sensor may detect the image of the complete FOV of theimaging system. However, for some applications the full azimuthal orzenithal angle range of the FOV may not be required. For suchapplications the 2D sensor may be arranged such that the central regionof the sensor is located outside the optical axis of the lens system.For sensors with a large aspect ratio, such a spatially “shifted”detection has the additional advantage that it can increase the fillfactor of the sensor. Another option is to combine two or more sensorswith smaller detection area for detecting the image. Non-relevant imageregions can thus be omitted during detection. The image can also bedetected by one or more 1D sensor arranged inside the image of the FOV.2D sensors and 1D sensors may also be used in combination.

In another preferred embodiment, a detection of the central region ofthe image is omitted by the sensor system. That means, the centralregion of the image is not detected by the sensor system and theelectronic image signal does not contain image information for thisregion. Therefore, the electronic image signal of the sensor will notinclude undesired image information which therefore must not beprocessed by the calculation electronics. Due to less information,energy can be saved and the calculations of the calculations electronicscan be accelerated.

In another preferred embodiment, the FOV preferably comprises zenithalangles between 80° and 100°, more preferably between 60° and 90° andeven more preferably between 90° and 120°. These preferred fields ofview correspond to a typical ZOI in a collision avoidance system.

In another preferred embodiment, the sensor system is combined with anemitter array. The sensor system and the emitter array may consist ofindividual elements or the sensor system and the emitter array form acombined transceiver system. A single lens system can therefore be usedas a two-way optics for the illumination system and the imaging systemof a conventional TOF depth sensing system. Using a single lens systemreduces costs, weight and size of a corresponding collision avoidancesystem. Moreover, a combined transceiver system may have lower costscompared an individual sensor systems and a corresponding emitter array.

In another preferred embodiment, the sensor system and the emitter arrayform a coherent transceiver. With coherent TOF depth sensing systems theeffective SNR can be increased compared to non-coherent systems suchthat higher detection efficiencies can be achieved even with lessemitted light power or at long distances.

According to another aspect of the invention, there is provided acollision avoidance system comprising an imaging system according to theinvention. A collision avoidance system is an electro-optical systemadapted to provide means and methods for detecting and preventingcollisions in a monitored environment. The collision avoidance systemcan be part of a security assistance system and may comprise as afurther component control electronics adapted to determine a possiblecollusion and to initiate suitable measures to avoid such a collision.Suitable measures may range from simply issuing a warning message up totaking over full control over a protected apparatus or system to avertany damage.

Further aspects of the invention could be learned from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in further detail. Theexamples given are adapted to describe the invention.

FIG. 1 shows calculated ray paths in a first embodiment of a lens systemaccording to the invention;

FIG. 2 shows calculated ray paths in a second embodiment of a lenssystem according to the invention;

FIG. 3 shows calculated ray paths in a third embodiment of a lens systemaccording to the invention;

FIG. 4 shows calculated ray paths in a fourth embodiment of a lenssystem according to the invention;

FIG. 5 shows calculated ray paths in a fifth embodiment of a lens systemaccording to the invention;

FIG. 6 shows calculated ray paths in further exemplary embodiments oflens systems according to the invention;

FIG. 7 shows illustrations of single 2D image sensors detecting areduced azimuthal angle range of the image;

FIG. 8 shows an illustration of using anamorphic distortion formaximizing the achievable image resolution;

FIG. 9 shows exemplary embodiments of a sensor system according to theinvention; and

FIG. 10 a schematic view of an exemplary embodiment of an imaging systemaccording to the invention.

DETAILED DESCRIPTION

FIG. 1 shows calculated ray paths in a first embodiment of a lens system10 according to the invention. The inset shows the definition of thezenithal angles ϕ and azimuthal angles θ with respect to the opticalaxis 12 of the lens system 10. The depicted lens system 10 is fullyrefractive and consists of 10 glass lenses. However, the number oflenses and the material type can be replaced with other quantities andmaterials. The lens system is designed for a zenithal field of view(FOV) of 20° starting at a zenithal angle of 80°. The minimum angle ofview (AOV) of the lens system 10 is thus 200°. All depicted rays arefocused onto a common image plane 16, which is perpendicular to thecentral optical axis 12 of the lens system 10.

The lens system 10 shown is specific in that the individual rays aredeflected from the FOV to the image plane 14 by four concave-convex(meniscus) lenses arranged in series, thus forming a deflecting lensstack. The rays from the FOV are transmitted only by the outer regionsof these lenses such that their diameter can be reduced from one lens tothe next in the direction of the image plane 14. The proposed shape ofthe convex-concave lenses can be easily produced and the adjustment ofthe lenses in the deflecting lens stack is simple compared toconfigurations including lenses with more complex lens shapes. Asfurther shown, an imaging system for the deflected rays is arrangeddirectly below the deflecting lens stack.

FIG. 2 shows calculated ray paths in a second embodiment of a lenssystem 10 according to the invention. The lens system 10 is fullyrefractive and consists of six plastic lenses. However, the number oflenses and the material type can be replaced by other quantities andmaterials. The lens system is designed for a zenithal FOV of 30°starting at a zenithal angle of 75°. The minimum AOV of the lens system10 is thus 210°. As it can be seen for the bundle of rays near thecenter of the lens system, rays under small zenithal angles are notfocused well in the image plane 14 while rays in the FOV a sharplyfocused in the image plane 14. However, by targeting the design for adesired zenithal FOV as a zone of interest (ZOI), the requirements for aplastic lens design are highly simplified such that the lens system 10can be designed in a less complex manner compared to glass-basedwide-angle lens systems 10.

The lens system 10 of this embodiment also comprises a deflecting lensstack arranged above an imaging system for the deflected rays. However,here only three lenses are included in the deflecting lens stack. Inparticular, the two outer convex-concave lenses of the lens stack inFIG. 1 are combined to a single convex-concave lens with a convexfreeform shape in the direction of the image plane 14. The inner lensmay preferably be a convex-concave lens or a plano-concave lens. Theproduction of a freeform element is more complex but allows implementingoptical correction directly to the deflecting lens stack. Thus, thetotal length of the lens system 10 can be decreased while good opticalimaging quality is maintained. On the other hand, due to a more complexlens shape, the adjustment effort may be slightly increased.FIG. 3 showscalculated ray paths in a third embodiment of a lens system 10 accordingto the invention. The depicted lens system 10 corresponds to the lenssystem 10 shown in FIG. 2 . Additionally a blind 18 covers the centralarea of the lens system 10 to block rays entering from the undesiredsmaller zenithal angles. However, a blind 18 can be used on any lenssystem 10 according to the invention. Preferably, the blind 18 can be acircular structure following the surface of the lens system on theobject side (so-called curved circular blind 18). Other shapes of theblind 18 are possible to allow an individual transmittance of additionalrays from selected zenithal angle ranges or to block specific azimuthalangle ranges. For example, a blind 18 can also be elliptically shaped orin the form of two circular blinds attached to one another along asection of their circumferences (with or without curvature). As a blind18 blocks rays entering from the smaller zenithal angles, only rays inthe FOV are focused in the image plane 14.

FIG. 4 shows calculated ray paths in a fourth embodiment of a lenssystem 10 according to the invention. The lens system 10 is acatadioptric lens system 10 comprising refractive and reflective opticalcomponents. The first component of the depicted lens system 10 is abiconcave lens element 40 in which object rays are reflected by a singletotal internal reflection 42 (TIR). Object rays in the FOV enter thelens element 40 from the side and are reflected at the inner surface onthe top of the lens element 40. In this embodiment, a zenithal FOV of30° is realized starting at a zenithal angle of 75°. Rays from outsidethe FOV are practically blocked as the condition for TIR and the concaveshape of the top surface of the lens element 40 are limiting theimageable zenithal angle range. An additional blind may thus not berequired for blocking undesired smaller zenithal angles.

In this lens system 10, the individual rays are deflected from the FOVto the image plane 14 by a single optical element, i.e., the biconcavelens element 40. The concave curvature of biconcave lens element 40 atthe side where the TIR occurs is adapted to directly deflect the raysfrom the FOV in the direction of the mage plane 14. The TIR region mayhave a parabolic or a freeform profile. The concave curvature ofbiconcave lens at the opposite side forms a dispersing lens for thedeflected rays and directs them to the related imaging system for thedeflected rays, which is arranged directly below. An advantage of such aconfiguration is that the adjustment process can be simplified and thesystem stability may be increased compared to systems comprising anumber of individual lenses, but at the expense of increased difficultyin the production of a correctly shaped biconcave lens element 40.Because the imageable zenithal angle range is intrinsically limited,scattered light can be reduced inside the lens system 10.

FIG. 5 shows calculated ray paths in a fifth embodiment of a lens systemaccording to the invention. Also this lens system 10 is a catadioptriclens system 10 comprising refractive and reflective optical components.The first component of the depicted lens system 10 is a complex freeformlens element 50 in which object rays are reflected by two total internalreflections 52, 54. Object rays in the FOV enter the freeform lenselement 50 from the side and are reflected first at the inner surface onthe bottom of the lens element 50 and second at the inner surface on thetop of the lens element 50. In this embodiment, a zenithal FOV of 30° isrealized starting at a zenithal angle of 75°. The lens element 50 isformed such that only rays in the FOV can enter the following parts ofthe lens system 10. In particular, the freeform shapes of the surfacesof the top and of bottom of the lens element 50 are designed such thatzenithal rays with angles not corresponding to the FOV are blocked. Alsoin this embodiment, an additional blind may not be required for blockingundesirable smaller zenithal angles.

In this lens system 10, the two total internal reflections 52, 54enhance the selectivity for rays from the FOV even more. Scattered lightor light incoming from other directions located outside the FOV can thuseffectively suppressed. The ray paths inside the lens element 50 cansimply be adapted to the required FOV. The lens element 50 can be acombination of thick spherical lens region at the circumference and twofreeform regions on the top and on the bottom of the lens element 50. Inparticular, the freeform region at the top of the lens element 50 may bea concave shape and the freeform shape at the bottom of the lens element50 may be convex shape. The central region of the bottom of the lenselement 50 may further include a lensing function for the rays directlydirected towards to image plane 14 and in particular the imaging systemfor the deflected rays. Besides reduced light scattering, anotheradvantage of this embodiment is the simple alignment and increasedstability resulting from the low total number of optical elements in thelens system 10. However, due to the two-fold ray path inside the lenselement 50, the diameter of the lens element 50 becomes large while thetotal length of the lens system 10 can be shortened compared to otherembodiments of the invention.

FIG. 6 shows calculated ray paths in further exemplary embodiments oflens systems 10 according to the invention. The depicted lens systems 10are similar to the lens system 10 shown in FIG. 1 , however, any lenssystem according to the invention could be applied. In the figuredifferent realizations of a zenithal FOV in such lens systems 10 areillustrated. The left lens system 10 has a zenithal angular range from60° to 90° corresponding to a FOV of 30°. The right lens system 10 showsa zenithal angular range from 90° to 120° which again corresponds to aFOV of 30° (minimum AOV is 240°). However, the position and the size ofthe FOV can be selected from a wide zenithal angular range. Preferredare zenithal fields of view between 20° to 40° which are selected in azenithal angular range starting from 60° and reaching up to more than150°.

FIG. 7 shows illustrations of single 2D image sensors 20 detecting areduced azimuthal angle range of the image 16. Detecting only a reducedazimuthal angle range may be desired when a full panoramic perspectiveis not required for a specific application. If the imaging system 10 isinstalled such that a part of the FOV is obscured and can thus not beused for imaging or collision avoidance, the sensor 20 may be shiftedalong the image plane in relation to the optical axis 12. Other optionsare to change the size of the senor 20 or adapting the lens system 10 tomaximize the area of detection on the sensor 20. In the leftillustration, the azimuthal FOV is around 270°, while in the rightillustration an azimuthal FOV of 180° is imaged on the sensor. In theillustrations, the smallest zenithal angles in the FOV are imaged at theinner border A of the image 16, while the largest zenithal angles in theFOV are imaged at the outer border B of the image 16. By limiting thedetected azimuthal angular range, the image resolution can be increasedby using the full detection area of the sensor 20 for the remainingazimuthal angular range.

FIG. 8 shows an illustration of using anamorphic distortion formaximizing the achievable image resolution. An axially symmetric lenssystem 10 images the FOV 16 as a circle in the image plane 14. Whenusing a single 2D sensor 20 with a rectangular detection surface, alarge number of pixels may not be used because of the different aspectratios of the image 16 and the senor 20. By using anamorphic distortionin the lens system 10, preferably by adding cylindrical and/or toroidallenses, the aspect ratios can be matched such that the image 16 can bedetected by a maximum number of pixels on the sensor 20. The appliedanamorphic distortion thus creates different magnifications in thehorizontal and vertical directions on the image sensor 20 in the imageplane 14, which provides an increased usage of the pixels on the imagesensor 20 and therefore allows better light collection. Furthermore,with a larger magnification, the resolution of the detection can beenhanced for the magnified regions in the image 16. Therefore, theimaging system 10 can be aligned such that some regions of the FOV maybe imaged with an increased optical quality.

FIG. 9 shows exemplary embodiments of a sensor system 20 according tothe invention. The sensor system 20 comprises at least a single 2Ddetector, at least a single 1D Detector or a combination thereof. Byselecting a specific type of sensor arrangement, the image can be fullyor partly comprised to allow a specialized detection of different partsof the image 16. The illustrations show how two or four rectangulardetectors can be used to detect the image 16. In all shown embodiments,a detection of the central region of the image 16 in the image plane 14is omitted by the sensor system 20. This saves costs, allows anincreased optical resolution and avoids a time- and energy-consumingprocessing of undesired information in the electronic image signal bythe calculation electronics 30.

FIG. 10 shows a schematic view of an exemplary embodiment of an imagingsystem 100 according to the invention. The depicted imaging system 100comprises a lens system 10, adapted for imaging angles of view largerthan 120° symmetrically around the optical axis 12 of the lens system 10in an image 16 on an image plane 14 perpendicular to the optical axis 12of the lens system 10; a sensor system 20, adapted to convert at least apart the image 16 in the image plane 14 into an electronic image signal;and an evaluation electronics 30, adapted to analyze the electronicimage signal and to output resulting environmental information; whereinthe lens system 10 and/or the sensor system 20 are designed forspecifically imaging fields of view starting at zenithal angles largerthan 80°.

LIST OF REFERENCE NUMBERS 10 lens system 12 optical axis 14 image plane16 image 18 blind 20 sensor system 30 evaluation electronics 40biconcave lens element 42 total internal reflection 50 complex freeformlens element 52 first total internal reflection 54 second total internalreflection 100 imaging system θ azimuthal angle ϕ zenithal angle AOVangle of view FOV field of view TOF time-of-flight ZOI zone of interestA, B borders of the imaged FOV

What is claimed is:
 1. An imaging system for time-of-flight depthsensing applications, comprising: a lens system including a deflectinglens stack configured to image angles of view larger than 120° in animage on an image plane and image fields of view starting at zenithalangles larger than 60°, wherein rays are transmitted only by outerregions of the deflecting lens stack such that diameters can be reducedfrom one lens to a next lens in the direction of the image plane; asensor system configured to convert at least a part of the image in theimage plane into an electronic image signal; and an evaluationelectronics configured to analyze the electronic image signal from thesensor system and to output resulting environmental information.
 2. Theimaging system of claim 1, wherein the deflecting lens stack includesmultiple concave-convex lenses.
 3. The imaging system of claim 2,wherein the multiple concave-convex lenses are arranged in series. 4.The imaging system of claim 1, wherein the deflecting lens stackincludes four concave-convex lenses.
 5. The imaging system of claim 1,wherein a central region of an entrance aperture of the lens system iscovered by a blind.
 6. The imaging system of claim 1, wherein at least asingle region other than the central region is covered by a blind. 7.The imaging system of claim 6, wherein selection of the at least singleregion is flexible.
 8. The imaging system of claim 1, wherein theevaluation electronics is configured to correct optical distortions inthe image signal and to output undistorted image information.
 9. Theimaging system of claim 1, wherein the lens system comprises plasticlenses, glass lenses or a combination thereof.
 10. The imaging system ofclaim 1, wherein the sensor system comprises at least a single 2Dsensor, at least a single 1D sensor or a combination thereof, whereinsuch a sensor is located outside an optical axis of the lens system. 11.The imaging system of claim 1, wherein a detection of the central regionof the image is omitted by the sensor system.
 12. The imaging system ofclaim 1, wherein the field of view comprises zenithal angles between 80°and 100°, between 60° and 90° or between 90° and 120°.
 13. The imagingsystem of claim 1, wherein the sensor system is combined with an emitterarray.
 14. The imaging system of claim 13, wherein the sensor system andthe emitter array forming a coherent transceiver.
 15. A collisionavoidance system comprising an imaging system imaging system fortime-of-flight depth sensing applications, the imaging systemcomprising: a lens system including a deflecting lens stack configuredto image angles of view larger than 120° in an image on an image plane,wherein rays are transmitted only by outer regions of the deflectinglens stack such that diameters can be reduced from one lens to a nextlens in the direction of the image plane; a sensor system configured toimage fields of view starting at zenithal angles larger than 60° andconvert at least a part the image in the image plane into an electronicimage signal and; and an evaluation electronics, adapted to analyze theelectronic image signal and to output resulting environmentalinformation.
 16. The imaging system of claim 15, wherein the sensorsystem comprises multiple sensors combined to omit non-relevant imageareas.
 17. The imaging system of claim 15, wherein the environmentalinformation includes an object identifier and a numerical value for adistance from a reference point to the recognized obj ect.
 18. Theimaging system of claim 15, wherein the lens system is optimized toprovide diffraction-limited imaging for all imaging points in the anglesof view.
 19. The imaging system of claim 15, wherein the deflecting lensstack includes multiple concave-convex lenses.
 20. The imaging system ofclaim 19, wherein the multiple concave-convex lenses are arranged inseries.